Abstract P418: PPARγ Targets both (Pro)Renin Receptor and Site-1 Protease in the Collecting Duct to Mediate Rosiglitazone-induced Fluid Retention

Abstract

Collecting duct (CD)-specific deletion of PPARγ attenuates the fluid retention side effect of thiazolidinedione including rosiglitazone (Rosi) but the underlying mechanism largely remains unknown. (Pro)renin receptor (PRR) is a newly described regulator of CD function. Recent results have demonstrated site-1 protease (S1P) but not furin or ADAM19 as the predominant PRR cleavage protease. A histidine-tagged soluble PRR, sPRR-His, stimulates AQP2 expression. Here, we examined involvement of PRR/S1P during Rosi-induced fluid retention. PRR promoter contains two putative PRREs at positions -834~-828 bp (AGGTTA) and -318~-312 bp (GGTGCA). A 2.0-kb mouse PRR promoter showed a 10-fold increase in luciferase activity in mpkCCD cells exposed to 10 μM Rosi. The Rosi-induced response was first mapped to -421~ -219 bp by the deletion analysis and then to the second PPRE by mutagenesis. Rosi treatment at 80 mg/kg diet in C57/BL mice rapidly induced a 1.9-fold increase in renal PRR protein, a 2.4-fold increase in urinary sPRR, a 2.0-fold increase in urinary renin activity, a 48% reduction of urine volume, and a 4.8-fold increase in renal AQP2 protein, without an effect on expression of ENaC subunits, at 36 h, all of which were diminished thereafter. On day 3, Rosi induced a 9% body weight gain (BWG) and a 15% reduction of Hct, a 20% increase of fluorescein isothiocyanate dextran (FITC-d)-measured plasma volume. In contrast, the indices of Rosi-induced fluid retention along with AQP2 upregulation were all nearly abolished by a PRR antagonist PRO20 and CD PRR deletion. The sensitivity to Rosi-induced volume expansion as assessed by Hct and FITC-d in the null mice was fully restored by a 3-d i.v. infusion of sPRR-His at 30 μg/kg/d. A 2.1-kb mouse S1P promoter also contained two PPRE sites and showed a 3-fold increase in luciferase activity in response to Rosi. Administration of a S1P inhibitor PF-429242 via minipump in C57/BL6 mice attenuated Rosi-induced FITC-d-measured plasma volume (Control 1.28 + 0.1 vs. Rosi 1.61 + 0.05 vs. Rosi + PF429242 1.37 + 0.08 ml/kg), BWG, and Hct drop. Overall, PPARγ simultaneously targets PRR and S1P to generate sPRR to increase AQP2 expression to expand plasma volume during Rosi treatment.